Re: [PATCH v1 03/11] mm: simplify hugetlb and file-THP handling in __page_mapcount()

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On 12/17/21 03:30, David Hildenbrand wrote:
> Let's return early for hugetlb, which really only relies on the compound
> mapcount so far and does not support PageDoubleMap() yet. Use the chance

It is too early to say if hugetlb double mapping will use PageDoubleMap().
I do not think (hope) it will be necessary.  So, I think you can drop mention
of it here.

> to cleanup the file-THP case to make it easier to grasp. While at it, use
> head_compound_mapcount().
> 
> This is a preparation for further changes.
> 
> Reviewed-by: Peter Xu <peterx@xxxxxxxxxx>
> Signed-off-by: David Hildenbrand <david@xxxxxxxxxx>

Acked-by: Mike Kravetz <mike.kravetz@xxxxxxxxxx>
-- 
Mike Kravetz

> ---
>  mm/util.c | 11 +++++++----
>  1 file changed, 7 insertions(+), 4 deletions(-)
> 
> diff --git a/mm/util.c b/mm/util.c
> index 741ba32a43ac..3239e75c148d 100644
> --- a/mm/util.c
> +++ b/mm/util.c
> @@ -732,15 +732,18 @@ int __page_mapcount(struct page *page)
>  {
>  	int ret;
>  
> -	ret = atomic_read(&page->_mapcount) + 1;
> +	if (PageHuge(page))
> +		return compound_mapcount(page);
>  	/*
>  	 * For file THP page->_mapcount contains total number of mapping
>  	 * of the page: no need to look into compound_mapcount.
>  	 */
> -	if (!PageAnon(page) && !PageHuge(page))
> -		return ret;
> +	if (!PageAnon(page))
> +		return atomic_read(&page->_mapcount) + 1;
> +
> +	ret = atomic_read(&page->_mapcount) + 1;
>  	page = compound_head(page);
> -	ret += atomic_read(compound_mapcount_ptr(page)) + 1;
> +	ret += head_compound_mapcount(page);
>  	if (PageDoubleMap(page))
>  		ret--;
>  	return ret;
> 





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